Juvenile hormone (JH) is an important regulatory element in Arthropod development and reproduction. However, our understanding of this hormone has centered almost exclusively on insects. In ticks, no endocrine gland has been unambiguously identified and the presence of JH is still hypothetical. This lack of basic information is an impedance to scientific research in this group. Considering the medical importance of ticks in disease transmission and the potential application of our knowledge of tick physiology in pest management, studies on identifying the tick JH should have significant practical value related to human health. In studies with the American dog tick, Dermacentor variabilis, we found that adult synganglia incubated in vitro with 3/H-methionine apparently released into the incubation medium JH III and the bisepoxide of JH III. Our earlier studies using RIA detected JH III in the hemolymph of blood fed adults but the bisepoxide was not investigated. A specific JH esterase was tentatively identified in nymphs and adults at the time of blood feeding which appeared to be involved in the removal of endogenous JH prior to the appearance of ecdysteroids. The objective of this proposal is to identify JH-like hormone(s) and the site of their biosynthesis in ticks. This will be achieved through in vitro incubations of individual tissues of D. variabilis during nymphal and adult development with radiolabeled precursors used to identify the insect JHs. The putative tick JH(s) will be identified by chromatography, chemical and enzyme derivatization, and GC-MS. JH(s) from the hemolymph of blood fed adults will be determined by GC-MS, and biological activity of the JH(s) assessed in ticks with several different bioassays. JH biosynthesis will be measured during nymphal and adult development and correlated with JH metabolism.